Method of synthesizing and processing carbon-supported, gold and gold-based multimetallic nanoparticles for use as catalysts

ABSTRACT

A method of preparing carbon-loaded, gold-based nanoparticle catalysts useful as anode catalysts for the electrocatalytic methanol oxidation reaction (MOR) as well as the oxygen reduction reaction (ORR). Au m Pt n M 100-m-n  catalysts may be prepared by either a two-phase protocol or by a thermal decomposition/reduction protocol. The prepared nanoparticles having different bimetallic ratios are assembled on carbon black support materials and activated by thermal treatment. This approach provides good control of nanoparticle size, composition and/or surface properties. Electrocatalytic MOR activities of the prepared and activated AuPt nanoparticle provided in accordance with the methods of the invention are present in both acidic and alkaline electrolytes.

RELATED APPLICATIONS

This application is related to co-pending U.S. patent application Ser.No. 11/051,777, filed Feb. 4, 2005 for GOLD-BASED ALLOY NANO-PARTICLESFOR USE AS FUEL CELL CATALYSTS, which is included by reference herein inits entirety.

FIELD OF THE INVENTION

The invention pertains to the synthesis and processing of nanoparticlesand, more particularly to the synthesis and processing ofcarbon-supported, gold and gold-based, highly monodispersed, highlyelectrocatalytic, monometallic, binary, and ternary nanoparticles.

BACKGROUND OF THE INVENTION

Electrochemical fuel cells convert chemical energy of fuels directlyinto electrical energy to provide a clean and highly efficient source ofelectrical energy. Like a battery, a fuel cell consists of twoelectrodes (an anode and a cathode) separated by an electrolytetypically made of a thin polymeric membrane. In a typical fuel cell,hydrogen gas from the fuel reacts electrochemically at the anodeelectrode and is converted into protons and electrons. The protons movethrough the electrolyte to the other electrode (i.e., the cathode),where they combine with the product from the reduction of oxygen fromthe air to form water, which is expelled from the cell as vapor. Theinvolvement of hydrogen and oxygen in the two reactions, one releasingelectrons and the other consuming them, yields electrical energy that istapped from across the electrodes.

Because of the high conversion efficiencies and low pollution, fuelcells such as hydrogen and direct methanol fuel cells are becomingincreasingly attractive power sources for mobile and stationaryapplications. Such applications include on-board electric power foradvanced propulsion systems for non-polluting vehicles. Whileresearchers around the world are developing potential fuel cellapplications including electric vehicles and portable electrical powersupplies, these developments face challenging scientific problems in theareas of materials science, interfacial science and catalysis. In protonexchange membrane fuel cells (PEMFCs), hydrogen ions must be transportedthrough a semi permeable membrane. Hydrocarbon fuels must first beconverted to pure hydrogen by reforming, and the overall conversionrequires complex process technology. In addition, substantialinvestments must be made in safety and controls.

Direct methanol fuel cells (DMFCs) offer a simpler solution and requireno reformer. Direct methanol fuel cells are increasingly considered anattractive power source for mobile applications because of the highenergy density, the fuel portability, and the easily renewable featureof methanol. The fuel portability of methanol is particularly importantin comparison with the difficulties of storing and transportinghydrogen.

In fuel cell reactions, both anode and cathode catalysts are veryimportant for many reasons.

Anode Catalysts:

The readily-obtainable energy density (approximately 2000 Wh/kg) andoperating cell voltage (0.4 V) for methanol fuel cells is presentlylower than the theoretical energy density (approximately 6000 Wh/kg) andthe thermodynamic potential (approximately 1.2 V) for such fuel cells.These problems are largely caused by poor activity of the anodecatalysts and “methanol cross-over” to the cathode electrode. Theseproblems account for a loss of about one-third of the available energyat the cathode and another one-third at the anode.

Pt-group metals have been extensively studied for both anode and cathodecatalysts, but a major problem is the ease with which they may bepoisoned by CO and CO-like intermediate species typically present.Binary PtRu nanoparticle catalysts on carbon supports are currentlyconsidered among the most promising catalysts. Binary PtRu catalystsexhibit a bifunctional catalytic mechanism in which Pt provides the mainsite for the dehydrogenation of methanol and Ru provides the site forhydroxide (OH) and for oxidizing CO-like species to CO₂.

Recently, gold at nanoscale sizes was found to exhibit unprecedentedcatalytic activities, both for CO oxidation and for electrocatalyticactivity for CO and methanol oxidation. Studies show that nanoscalegold-based bimetallic materials may provide a synergistic catalyticeffect for the methanol oxidation reaction (MOR) at the anode inmethanol oxidation fuel cells. For example, the synergistic catalyticeffect of gold-platinum (AuPt) nanoparticles might suppress adsorbedpoisonous species by changing the electronic band structure to modifythe strength of the surface adsorption.

While bimetallic AuPt is a known electrocatalyst for oxygen reduction inalkaline fuel cells, few reports concern utilizing AuPt nanoparticleswith controllable size and composition in fuel cell catalystapplications. In such bimetallic systems, Pt could provide the mainhydrogenation or dehydrogenation sites, while Au together with Pt couldspeed up the removal of poisonous species. In the past, decreasingactivation energy to facilitate oxidative desorption and suppressingadsorption of CO were believed to lead to sufficiently-high adsorptivityto support catalytic oxidation in alkaline electrolytes. However, it hasrecently been shown that catalysts prepared by impregnation from Pt andAu precursors provided results similar to those of monometallic Ptcatalysts, suggesting that the presence of Au did not significantlyaffect the catalytic performance of Pt. This is attributed tophase-segregation of the two metals due to their miscibility gap. Assuch, only Pt participates in the adsorption of CO and the catalyticreaction. How the bimetallic catalytic properties depend on nanoparticlepreparation and composition is an important area for the development ofnew or improved catalysts for fuel cell research.

Cathode Catalysts:

As previously stated, both the energy density and operating cell voltagefor direct methanol fuel cells are currently much lower than values thatare theoretically possible. At the cathode, the kinetic limitation ofthe oxygen reduction reaction (ORR) is a problem of interest in protonexchange membrane fuel cells operating at low temperature (<100° C.) andin DMFCs. The rate of breaking O═O bonds to form water strongly dependson the degree of the oxygen interaction with the adsorption sites of thecatalyst and competition with other species in the electrolyte (e.g.,CH₃OH). There is also strong adsorption of OH forming Pt—OH, whichcauses inhibition of the O₂ reduction.

The present inventors have recently investigated gold and gold alloynanoparticles as potential electrocatalysts fuel cell reactions such asCO and methanol oxidation reactions and oxygen reduction reactions. Theexploration of gold nanoparticles in catalysis shows potentialapplications in fuel cell related catalytic reactions. The nanoparticlesurface properties are essential for the adsorption of oxygen and thecatalytic reaction of gold at nanoscale sizes. Bimetallic AuPtcomposition may produce a synergistic catalytic effect that involves thesuppression of adsorbed poisonous species and the change in electronicband structure to modify the strength of the surface adsorption for ORR.

The study of AuPt binary and AuPtM ternary nanoparticles withcontrollable size and composition for fuel cell catalyst applications isimportant because metal nanoparticles in the size range of approximately1-10 nm undergo a transition from atomic to metallic properties, and thebimetallic composition could produce synergistic effect. For example,for the adsorption of (OH⁻)_(ads) (i.e., OH⁻ species adsorbed on thecatalyst surface) in an alkaline medium the presence of Au in Ptcatalysts could reduce the strength of the Pt—OH formation. A fullunderstanding of how the synergistic catalytic effect operates at thenanoscale gold and gold-platinum surface remains elusive. Gold-basedbinary (AuPt) and ternary (AuPtM) nanoparticles of 1-10 nm core sizeswith controllable Au, Pt and a third metal (M), for example, M=W, Ti,Cr, Fe, Mn, etc. have been prepared. These nanoparticles may beassembled onto high surface area carbon nanomaterials with controlleddispersion and loading. The carbon-supported AuPt/C or AuPtM/Cnanoparticles are processed by thermal treatment to achieve desiredcharacteristics including size, composition and alloy properties. Theelectrocatalytic activity of such thermally treated, carbon-supportednanoparticles may be evaluated in both methanol oxidation reactions(MOR) and oxygen reduction reactions (ORR).

The introduction of the third metal component into the binarynanoparticles forms AuPtM ternary nanoparticles. Ternary nanoparticlesare expected to lead to several important modifications of the catalyticproperties, possibly including further modification of the electronicstructure, introduction of an oxide component on the catalyst surfacevia the propensity of oxide formation of the metal component, andcontrol of the size increase during thermal treatment via alloying withthe metal. The relatively low cost of the third component metal shouldhelp lower the cost of catalyst materials. Metals such as W, Ti, Pt, Cr,Fe, and Mn, all having melting points higher than Au may be used toprepare AuPtM nanoparticle catalysts. The research is coupled withcombinatorial knowledge base for better design of binary and ternarynanoparticles with controllable size, composition and phase properties.The binary/ternary catalysts can be used not only as methanol-tolerantcathode catalysts in fuel cell membrane electrode assemblies (MEAs), butalso as CO-tolerant catalysts in combination with the desired oxidesupport materials for water-gas shift reactions.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a new methodof preparing carbon-loaded, gold-based, nanoparticle catalysts. Suchcatalysts are known to be useful anode catalysts for theelectrocatalytic methanol oxidation reaction (MOR) as well as the oxygenreduction reaction (ORR). Au_(m)Pt_(n)M_(100-m-n) catalysts may beprepared by either a two-phase protocol or by a thermaldecomposition/reduction protocol. The prepared nanoparticles areassembled on carbon black support materials and activated by thermaltreatment. Nanoparticles having different bimetallic ratios areassembled on carbon black support materials and activated by thermaltreatments at different temperatures. This approach provides a bettercontrol of nanoparticle size, composition and/or surface properties incomparison with traditional approaches such as co-precipitation,deposition-precipitation, and impregnation. Electrocatalytic MORactivities of the prepared and activated AuPt nanoparticle provided inaccordance with the methods of the invention are present in both acidicand alkaline electrolytes.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the present invention may be obtained byreference to the accompanying drawings when considered in conjunctionwith the subsequent detailed description, in which:

FIG. 1 a is a TEM micrograph of approximately 2 nm diameter Aunanoparticles;

FIG. 1 b is a TEM micrograph of approximately 2 nm diameter Au/Cnanoparticles;

FIGS. 1 c and 1 d are TEM micrographs of the Au/C nanoparticles of FIG.1 b treated at 250° C. and 300° C., respectively;

FIGS. 2 a and 2 b are a representative TEM micrograph and a sizedistribution for Au₇₂Pt₂₈ nanoparticles, respectively;

FIG. 2 c is a TEM micrograph showing Au₇₂Pt₂₈ nanoparticles assembledonto carbon black;

FIGS. 2 d and 2 e show TEM micrographs of Au₇₂Pt₂₈/C nanoparticlestreated at 400° C. and 500° C., respectively;

FIGS. 3 a and 3 b are a representative TEM micrograph and a sizedistribution for Au₈₂Pt₁₈ nanoparticles, respectively;

FIG. 3 c is a TEM micrograph showing Au₈₂Pt₁₈ nanoparticles assembledonto carbon black;

FIGS. 3 d and 3 e show TEM micrographs of Au₈₂Pt₁₈/C nanoparticlestreated at 400° C. and 500° C., respectively;

FIG. 3 f is a high-resolution TEM micrograph of a single one of theAu₈₂Pt₁₈/C nanoparticles of FIG. 3 e;

FIG. 4 is a representative TEM micrograph for Au₁₁Pt₂₃Fe₆₆nanoparticles;

FIG. 5 is a graph of lattice structure parameters for Au_(m)Pt_(100-m)/Cnanoparticles vs. percentage of Au in the composition;

FIG. 6 a is a plot of FTIR spectra of CO adsorption for Au/SiO₂ treatedat 200 (black), 400° C. (red), and SiO₂ blank (blue) (Spectra werecollected in the presence of 4% CO in N₂);

FIG. 6 b is a plot of FTIR spectra of CO adsorption for Au/SiO₂ treatedat 200 (black), 400° C. (red), and SiO₂ blank (blue) (Spectra werecollected in the pure N₂ following purging CO away);

FIG. 6 c is a plot of FTIR spectra of CO adsorption for Pt/SiO₂,Au/SiO₂, & Au_(n)Pt_(100-n)/SiO₂ with 4% CO;

FIG. 6 d is a plot of FTIR spectra of CO adsorption for Pt/SiO₂,Au/SiO₂, & Au_(n)Pt_(100-n)/SiO₂ with pure N₂. Solid lines: experimentaldata. Dash lines: spectral deconvolution;

FIGS. 7 a and 7 b are typical sets of cyclic-voltammetric (CV) curvesobtained for a MOR in alkaline electrolyte (solid lines: with methanol;dot lines: without methanol) on Au₈₂Pt₁₈/C catalysts (20% metalsloading) at treatment temperatures of 400° C. and 500° C., respectively;

FIGS. 8 a-8 d are representative sets of CV curves comparing theelectrocatalytic MOR characteristics of Pt/C, PtRu/C, Au₈₂Pt₁₈/C, andAu/C catalysts in 0.5M KOH with (solid lines) and without (dot lines)0.5 M methanol;

FIG. 9 a is a typical CV curve for Au₇₂Pt₂₈/C catalysts treated at, 400°C. (dot lines) and 500° C. (solid lines), in 0.5 M KOH saturated with O2(thick curves) and Ar (thin curves);

FIG. 9 b is a typical CV curves for Au₇₂Pt₂₈/C catalysts treated at 400°C. (dot lines) and 500° C. (solid lines), in 0.5 M H₂SO₄ saturated withO2 (thick curves) and Ar (thin curves);

FIG. 10 is a chart and overlaid plot showing mass activities from RDEmeasurements for an ORR in 0.5M KPH vs. a bimetallic composition;

FIG. 11 a is a series of RDE plots (1600 rpm) for AuPt/C and AuPtFe/Ccatalysts in 0.5 M KOH electrolyte saturated with O2;

FIG. 11 b is a series of RDE plots for AuPt/C and AuPtFe/Ccatalysts in0.5 M H₂SO₄ electrolyte saturated with O₂; and

FIG. 12 is a plot of the relationship of Au percentage in the feedstockand the gold percentages in the resulting nanoparticles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides new methods of preparing andcharacterizing gold and gold-based nanoparticles for use as fuel cellcatalysts.

Catalyst Preparation and Characterization:

Three different types of nanoparticles were synthesized. First, Aunanoparticles having 2 nm diameter core sizes and encapsulated with analkanethiolate monolayer shell were synthesized by a standard, two-phasemethod known to those of skill in the art.

In addition, Au nanoparticles having approximately 2 nm diameter coresizes and encapsulated with an alkanethiolate monolayer shell weresynthesized by a modified two-phase method known to those of skill inthe art. One such modified, two-phase method used is briefly described.AuCl₄ ⁻ and PtCl₆ ²⁻ are first transferred from aqueous solution ofhydrogen tetrachloroaurate (HAuCl₄) (0.64 g) and hydrogenhexachloroplatinate (IV) (H₂PtCl₆) (0.66 g) into toluene solution usinga phase transfer reagent such as tetraoctylammonium bromide. Thiols (1.4mL decanethiol, DT) and oleylamine (1 mL, OAM) are then added to theorganic solution, and an excess of aqueous NaBH₄ (2.0 g) is slowly addedfor the reaction. The produced DT-encapsulated AuPt nanoparticles intoluene are evaporated for removing solvent, and then dissolved inethanol. After being centrifuged, the precipitated product may becollected and dissolved in hexane. As may be seen in FIG. 12, there isan approximately linear relationship between the percentage of Au in thesynthetic feed stock and the percentage of gold in the formednanoparticles.

Finally, AuPtFe nanoparticles are synthesized using a thermaldecomposition/reduction protocol. Briefly, a certain amount of platinumacetylacetonate (Pt(acac)₂) and dimethyl (acetylacetonate) gold (III)((CH₃)₂ (C₅H₇O₂)Au) or gold (III) acetate, AuCl(SC₄H₈) are added to anoctyl ether solution containing a reducing agent such as1,2-hexadecanediol while the solution is stirred. After the solution isheated to 105° C., iron pentacarbonyl (Fe(CO)₅) and capping agents(oleylamine and oleic acid) are then added to the solution. The mixtureis heated to a temperature greater than 200° C. and refluxed for 30 min.After the reaction mixture is allowed to cool to room temperature, thenanoparticles may be precipitated and cleaned by adding ethanol. Thecomposition of the resulting AuPt and AuPtFe nanoparticles may then bedetermined using a Direct Current Plasma-Atomic Emission Spectrometer(DCP-AES).

Carbon black XR-72c in the form of approximately 30-50 nm diameterspheres is used as a support for the nanoparticles. A controlled amountof Au or AuPt nanoparticles is added to the suspension of carbon black,which is then sonicated and the mixture is then stirred overnight. Theloading of Au or AuPt particles on the carbon supports may be controlledby the weight ratio of Au or AuPt nanoparticles to carbon black. Theactual loading of metals may be determined by Thermogravimetric Analysis(TGA) and DCP-AES analysis. Similar protocols may be used for assemblingthe nanoparticles on silica (SiO₂) support materials.

The carbon- or silica-loaded nanoparticle catalysts are next treated ina tube-furnace by heating at approximately 300° C. under 20% O₂/N₂ forapproximately 1 hour followed by treatment at 400° C. or 500° C. under15% H₂/N₂ for approximately 2 hours. The different results obtained bytreating at 400° C. or 500° C. are discussed in detail hereinbelow.While standard temperatures of 400° C. or 500° C. have been used inthese studies, it will be recognized that a broad range of treatmenttemperatures may beneficially be used. Temperatures in the range ofbetween approximately 250° C. and 650° C. appear usable.

Electrode:

Electrodes may be prepared using the following method. Glassy carbon(GC) disks (geometric area: 0.07 cm² for cyclic voltammetric measurementand 0.20 cm² for rotating disk electrode measurement) are polished with0.03 μm Al₂O₃ powders to a “mirror” finish. Such electrode preparationtechniques are considered known to those of skill in the art and are notfurther described herein. The geometric area of the substrate electrode(glassy carbon), not the surface area of the catalyst itself, provides ameasure of the loading of catalyst on the electrode surface used for thevoltammetric characterization. A typical suspension of the catalysts maybe prepared by suspending 1 mg of the catalyst in 1 mL of 0.25% Nafion®solution and then sonicating the suspension for approximately 15minutes. The resulting suspension has been found to remain stable fordays. The suspension may then be quantitatively transferred to thesurface of the polished GC disks. The electrodes are then typicallydried overnight at room temperature.

Measurements:

The cyclic voltammetry and rotating disk electrode measurements are bothperformed at room temperature. All experiments are performed inthree-electrode electrochemical cells. All electrolytic solutions aredeaerated with high purity argon or nitrogen before the measurements.All measured potentials are with respect to a reference electrode ofAg/AgCl saturated KCl, which is +0.20 V with respect to a normalhydrogen electrode (NHE) reference. The cyclic voltammetric measurementsare performed by using a microcomputer-controlled potentiostat such asan EG&G Instruments/Princeton Applied Research Model 273. The rotatingdisk electrode (RDE) measurements are performed using a rotating diskelectrode measurement system such as Pine Instrument Model AFCBP1.

The composition analysis may be performed using an ARL Fissions ModelSS-7 DCP-AES. Measurements are made on emission peaks at 267.59 nm,265.95 nm, and 259.94 nm for Au, Pt, and Fe, respectively. Thenanoparticle samples are first dissolved in concentrated aqua regia, andthen diluted to concentrations in the range of 1 to 50 ppm for analysis.Calibration curves are made from dissolved standards with concentrationsranging from 0 to 50 ppm in the same acid matrix as the unknown samples.Detection limits, based on three standard deviations of the backgroundintensity, are 0.008 ppm, 0.02 ppm, and 0.005 ppm for Au, Pt, and Fe.Standard samples and unknown samples were each analyzed 10 times eachfor 3 second counts. Instrument reproducibility, for concentrationsgreater than 100 times the detection limit, resulted in errors less than±2%. For example, DCP analysis of the bimetallic nanoparticlessynthesized under a particular condition indicated an atomic compositionof 72% Au and 28% Pt. Consequently, the nanoparticles of this particularcomposition are denoted Au₇₂Pt₂₈.

Transmission electron microscopy (TEM) was performed using a HitachiModel H-7000 electron microscope (100 kV). For TEM measurements, AuPt,AuPt/C, or AuPtFe/C samples were suspended in a hexane solution and weredrop cast onto a carbon-coated copper grid followed by solventevaporation in air at room temperature.

Thermogravimetric analysis (TGA) for determining the metal loading oncarbon black was performed on a Perkin-Elmer Model Pyris 1-TGA. Typicalsamples weighed approximately 4 mg and were heated in a platinum pan.Samples were heated in 20% O₂ at a rate of approximately 10° C./min.

The thermally treated nanoparticles were examined by powder X-raydiffraction (XRD). Powder diffraction patterns were recorded on aScintag Model XDS 2000 θ-θ powder diffractometer equipped with a Ge(Li)solid state detector (CuK. radiation). The data were collected from 10°to 90° 2θ at a scan rate of 0.02° 2θ per step and 30 seconds per point.

Results:

Referring first to FIGS. 1 a-1 d, there are shown TEM micrographs of 2nm Au nanoparticles, Au_(2-nm)/C assembled nanoparticles before thermaltreatment, and Au_(2-nm)/C nanoparticle treated at 250° C. and 300° C.,respectively.

Referring now to FIGS. 2 a and 2 b, there are shown a representative TEMmicrograph and a size distribution for Au₇₂Pt₂, nanoparticles,respectively. The relatively uniform inter-particle spacing (FIG. 2 a)shows that the particles are individually-isolated by their cappingmonolayers. This conclusion is also supported by FTIR detection ofvibrational bands characteristic of the capping molecules. Thenanoparticles displayed an average size of 1.8 nm with a relatively sizemonodispersity (±0.4 nm) (FIG. 2 b). The Au₇₂Pt₂₈ nanoparticles, whenassembled onto carbon black, also showed a very good dispersion, and theaverage size of the particles showed little change. This may be seen inFIG. 2 c. The capping or linking shells remain intact and areresponsible for the interaction with the carbon surfaces.

As stated hereinabove, the thermal treatment involved heating thecatalyst at 300° C. under 20% O₂ followed by treatment at 400° C. or500° C. in 15% H₂. After the thermal treatment of the carbon-loadedcatalysts, the average particle size was found to increase. The sizeincrease appears to be dependent upon the treatment temperature.

Referring now to FIGS. 2 d-2 e, there are shown TEM micrographs ofAu₇₂Pt₂₈ nanoparticles treated at 400° C. and 500° C., respectively. Theaverage size of Au₇₂Pt₂₈ nanoparticles increased to 4.6±1.0 nm aftertreatment at 400° C. (FIG. 2 d) and to 4.6±1.2 nm after treatment at500° C. (FIG. 2 e).

Referring now to FIGS. 3 a and 3 b, there are shown a representative TEMmicrograph and a size distribution for Au₈₂Pt₁₈ nanoparticles,respectively. The relatively uniform inter-particle spacing (FIG. 3 a)shows that the particles are individually-isolated by their cappingmonolayers. This conclusion is also supported by FTIR detection ofvibrational bands characteristic of the capping molecules. Thenanoparticles displayed an average size of 1.8 nm with a relatively sizemonodispersity (±0.6 nm) (FIG. 3 b). The Au₈₂Pt₁₈ nanoparticles, whenassembled onto carbon black, also showed a very good dispersion, and theaverage size of the particles showed little change. This may be seen inFIG. 3 c. The capping or linking shells remain intact and areresponsible for the interaction with the carbon surfaces.

FIGS. 3 d-3 e are TEM micrographs of Au₈₂Pt₁₈ nanoparticles on carbonsupport after thermal treatment at 400° C. and 500° C., respectively.The average size of Au₈₂Pt₁₈ nanoparticles increased to 3.3±1.1 nm andto 3.9±1.1 nm after the treatments at 400° C. and 500° C., respectively.It is believed that local mobility of the shell-removed nanoparticles oncarbon surface is responsible for the size increase.

FIG. 3 f is a high resolution TEM micrograph of a single nanoparticle asseen in FIG. 3 e.

Referring now to FIG. 4, there is shown a TEM micrograph of Au₁₁Pt₂₃Fe₆₆nanoparticle catalyst.

The effective removal of the capping agents may be verified by both FTIRand XPS analyses of the catalyst. After successful removal of thecapping agents, the vibrational bands characteristic of the cappingmolecules in the C—H stretching region are no longer detected by FTIR.XPS analysis also shows that the bands associated with sulfur speciesare absent after successful thermal treatment.

Thermally treated AuPt bimetallic nanoparticles may be analyzed usingXRD techniques. It is believed that the ability to control thecomposition and phase properties of bimetallic nanoparticles is criticalto their future use as catalysts. The bimetallic nanoparticles formed inaccordance with the inventive method display alloy properties. This isvery different from the bimetallic miscibility gap generally seen in thebulk counterparts of the bimetallic metals. This finding demonstratesthe difference between both the physical and chemical properties ofnanoscale materials compared with the properties of the same materialsin a bulk, crystalline state. Important details of the phase propertiesof the bimetallic nanoparticle catalysts and new information correlationbetween the nanoparticle composition and the phase properties of thatmaterial at the nanoscale have also been discovered.

Referring now to FIG. 5, there is shown graph of lattice structureparameters for Au_(m)Pt_(100-m)/C nanoparticles vs. percentage of Au inthe composition. As may be seen, there is an approximately linear fit tothe experimental data.

The lattice parameters of several AuPt nanoparticles scale linearly withthe relative Au/Pt content (i.e., follow a Vegard's type law typicallyobserved with binary metallic alloys). The correlation between the phasetype and the bimetallic composition at the nanoscale therefore isdifferent from bimetallic composition counterparts. The bulkcounterparts typically display a miscibility gap manifested by a breakin the linear correlation between the lattice parameter and thecomposition at approximately 10-80% Au. Within the miscibility gap, thelattice parameters of bulk AuPt are independent of the composition.

Understanding the surface properties of gold-based alloy nanoparticlesis believed essential to exploiting their unique catalytic properties.To probe these properties, FTIR was used to investigate CO adsorption onthe surface of silica-supported gold-platinum nanoparticles. Thenanoparticles were assembled on silica supporting materials, and treatedat controlled conditions. By comparing the spectroscopic characteristicswith those of the monometallic nanoparticle counterparts, the COstretching bands for the adsorption on the bimetallic nanoparticlecatalysts may be seen to fall distinctively between those for themonometallic Au and Pt nanoparticle catalysts. This verifies the surfacealloy character of the bimetallic nanoparticle catalysts. These newinsights into the correlation between the bimetallic composition and thesurface binding properties and their implications to the design ofgold-based bimetallic nanoparticle catalysts are discussed in detailhereinbelow.

One important question is whether the surface metal distribution isdifferent from the composition in the multimetallic nanocrystals. If itis different, it is important to understand how the surface bindingsites impact the surface adsorption or catalytic activity. To answerthese questions, CO is used as an in situ FTIR probe because thestretching band for the adsorption of CO on nanocrystal surfaces ishighly sensitive to surface binding sites in terms of composition andgeometry. FIG. 6 shows a set of data. For Au/SiO₂ (FIG. 6 a-6 b), thedetection of the peak at 2129 cm⁻¹ is consistent with literaturereports. However, the spectral difference due to treatment temperaturesdemonstrated that the surface properties for Au catalysts is highlydependent on the thermal treatment. While traces of contaminants mayexist in silica treated in the same manner, the observed signals areapproximately one order of magnitude lower than those of the catalystand do not significantly contribute to the detected bands.

In contrast to the features characteristic of the monometallic Au andphysical mixture of Au and Pt, the CO band for AuPt alloys is unique andfalls in between those for the two monometallic catalysts (FIGS. 6 c-6d). As may readily be seen, the 2129 cm⁻¹ band is greatly diminished.The surface binding sites on the bimetallic nanoparticles are clearlymodified as a result of the surface alloying of the two components. Anapparent red shift of approximately 15 cm⁻¹ with increasing treatmenttemperature was also detected. This probably indicates a re-distributionof the relative bimetallic composition on the nanocrystal's surface,leading to a surface enrichment of Au. The absence of phased-segregationfor the bimetallic Au₇₂Pt₂₈ and Au₈₂Pt₁₈ catalysts, as demonstrated bythe XRD data, substantiates the effectiveness of the novel preparationmethod of the present invention when compared to data reported for COadsorption on dendrimer-derived gold-platinum nanoparticles.

In addition, X-ray Photoelectron Spectroscopy (XPS) is utilized to probethe relative composition in the multimetallic nanoparticles upon thethermal treatment, and to determine composition and relative surfaceenrichment of a specific element. The results from XPS studies of AuPtand AuAg alloy nanoparticles have demonstrated the viability ofdetecting the relative change of the bimetallic composition, and moreimportantly, the effective removal of the capping materials. Forexample, no sulfur was detected for the AuPt/SiO₂ sample treated at 400°C.

TABLE 1 Comparison of CO bands on monometallic and bimetallic catalysts.Peak Position (cm⁻¹) Sample (on SiO₂) 0 1 2 3 4 5 Au (400° C.) 2129 20471999 1942 Au (500° C.) 2129 2042 1988 1901 Pt (400° C.) 2091 2079 20491854 (sh) mixed Au/ & Pt/SiO₂ 2091 2078 2045 1989 1866 (400° C.) (sh)Au₇₂Pt₂₈ (400° C.) 2088 2065 2030 1990 1867 (sh) (sh) (sh) Au₇₂Pt₂₈(500° C.) 2067 2035 1996 1877 (sh) (sh) Au₈₂Pt₁₈ (400° C.) 2098 20542027 2001 1879 (sh) (sh) (sh) Au₈₂Pt₁₈ (500° C.) 2057 2033 1988 1887(sh) (sh) Note: Bold numbers indicate primary peaks, (sh) for shoulderband.

As may be seen from both the plots of FIG. 6 d and the data of Table 1,physically-mixed Au/SiO₂ and Pt/SiO₂ (FIG. 6 d, plots B and A,respectively) catalysts showed features characteristic of monometalliccatalysts as shown by peaks of 0, 1, 2, 3, 4, and 5 in their respectiveplots. However, thermally treated AuPt catalysts have bimetallic alloycharacteristics at the surface as may been seen by the fact that thepeaks are falling in between peaks 2 and 3. This result is due to thefact that the CO band is unique and falls between those for the twomonometallic catalysts.

Overall, the CO adsorption bands for the bimetallic AuPt catalysts fallbetween the two monometallic catalysts. This result is quite differentfrom prior art findings regarding CO adsorption on AuPt catalystsprepared in accordance with a dendrimer-based synthesis protocol. COadsorption bands from nanoparticles so prepared fell within the bulkmiscibility gap.

The bimetallic Au₇₂Pt₂₈ and Au₈₂Pt₁₈ catalysts show other alloyproperties, not properties of phased-segregated metals. This is inagreement with the observed XRD data.

The adsorption of CO on the silica-supported bimetallic AuPtnanoparticle catalysts displays CO stretching bands which falldistinctively between those observed for silica-supported monometallicAu and Pt nanoparticle catalysts. The detection of such CO bandsdemonstrates that the CO binding properties of the bimetallicnanocrystal's surface are highly dependent on the bimetalliccomposition, the treatment temperature, and other preparationconditions. These findings further substantiate the alloy character ofthe surface binding sites of the bimetallic nanoparticle catalystsprepared in accordance with the inventive method.

The electrocatalytic activity of the carbon-supported catalysts loadedon glassy carbon electrode is characterized for both MOR and ORR, inboth acidic and alkaline electrolytes. Some examples are provided.

The electrocatalytic activity of the Au₈₂Pt₁₈/C catalysts loaded onglassy carbon electrode was characterized for a MOR reaction in bothacidic and alkaline electrolytes. While the results from the acidicelectrolyte show relatively low electrocatalytic activity, significantelectrocatalytic activity may be observed in an alkaline electrolyte.

Referring now to FIGS. 7 a and 7 b, there are shown two typical sets ofcyclic-voltammetric (CV) curves obtained for MOR in alkaline electrolyteon Au₈₂Pt₁₈/C catalysts (20% metals loading). The catalysts were treatedat two different treatment temperatures, 400° C. (FIG. 7 a) and 500° C.(FIG. 7 b). Measurements were performed with the catalyst on a 0.07 cm²GC electrode, at a scan rate of 50 mV/s, and 0.5M KOH electrolyte.Measurements were made with 0.5 M methanol (solid curves) and withoutmethanol (dashed curves). All data is with reference to an Ag/AgClreference electrode.

The peak potentials and peak currents provided measures of theelectrocatalytic activity are summarized in Table 2.

TABLE 2 Comparison of peak potential (E_(pa)) and peak current (i_(pa))for MOR at AU₈₂Pt₁₈/C catalysts. Metal Treatment Activity in 0.5 M KOHloading temperature i_(pa) (mA/cm²/mg Wt % ° C. E_(pa) (mV) Metal) 20%400 −160 6518 20% 500 −171 8536 Electrode coverage, 57 μg(metals/C)/cm². Concentration of methanol: 0.5 M; Electrode area: 0.07cm²; Scan rate: 50 mV/s; Ref electrode: Ag/AgCl, Saturated KCl.

In the absence of the methanol in the electrolyte, both catalysts (FIGS.7 a, 7 b) exhibit redox waves corresponding to gold and gold oxide onthe surface. The gold oxidization wave was found at approximately 0.3 Vwhereas the reduction wave was located at approximately 0.06-0.07 V forboth catalysts. There seems to be a subtle difference in the redoxcurrent, which is perhaps suggestive of surface composition differences.The Au₈₂Pt₁₈/C catalysts treated at 500° C. showed larger redox currentsfor gold than those treated at 400° C. In comparison with the data fromthe above control experiment (dashed lines), a large anodic wave appearsat −0.16 V or at approximately −0.17 V for catalysts treated at 400° C.(FIG. 7 a) and 500° C. (FIG. 7 b), respectively, in the presence ofmethanol. This anodic wave corresponds to the electrocatalytic oxidationof methanol.

FIGS. 8 a-8 d show representative sets of CV curves comparing theelectrocatalytic MOR characteristics of Pt/C (E-Tek), PtRu/C (E-Tek),Au₈₂Pt₁₈/C, and Au/C catalysts, respectively, on 0.07 cm² GC electrodes,in 0.5M KOH with 0.5 M methanol (solid curves), and without methanol(dashed curves). All data were obtained with 20% metal loading and thescan rate was 50 mV/s.

As may be seen in FIGS. 8 a-8 d, the peak potentials of the Au₈₂Pt₁₈/Ccatalysts (FIG. 8 c) are more negative than those for a monometallic Aucatalyst Au/C (FIG. 8 d).

As may be seen in FIGS. 7 a and 7 b, the magnitude of the anodic currentfor the AuPt/C treated at 500° C. is greater than that treated at 400°C. Furthermore, a smaller anodic wave is observed at approximately −20mV on the reverse sweep for the AuPt/C catalysts. This anodic wave isbelieved to be attributable to the oxidation of methanol on are-activated catalyst surface. For the comparison, 20% Au/C, 20% AuPt/C,20% Pt/C and 20% PtRu/C catalysts were studied under the sameconditions. The catalyst thin films on the GC electrode were alsoprepared under the same conditions.

It is evident that the general electrocatalytic characteristic forAuPt/C catalysts is quite similar to those observed for the Pt/C andPtRu/C catalysts. By comparing peak potentials and peak currents, it canbe seen that the peak potential for AuPt/C catalysts is higher byapproximately 10-20 mV compared to Pt/C and by approximately 80-100 mVcompared to PtRu/C. The peak current density of the AuPt/C catalyst,after being normalized to the total metal loading, is larger than thatfor PtRu/C catalyst and slightly smaller than Pt/C catalyst. Thisobservation indicates that there is a major improvement in comparisonwith that of Au/C catalysts in terms of the peak potential (byapproximately −600 mV) and the peak current (by approximately 25×). Thepresence of a small fraction of Pt in the Au-based bimetallicnanoparticles significantly modifies the catalytic properties thereof.

The catalytic modification of the bimetallic composition is, in fact,further supported by the remarkable difference in the voltammetriccharacteristics observed in the reverse scan, especially in the alkalineelectrolyte. For Pt/C and PtRu/C, the reverse wave for alkalineelectrolyte occurs at a potential less positive than the forward wave byapproximately 200 mV. In contrast, the reverse wave for AuPt/C occurs ata potential which differs from the potential for the wave in the forwardsweep by only approximately 20 mV. The relative peak current of thereverse/forward wave is also found to be dependent on the percentage ofAu in the bimetallic nanoparticles. The oxides formed on the catalystsurface at the potential beyond the anodic peak potential in thepositive sweep are reduced in the reverse sweep. Poisonous CO speciesformed on the Pt surfaces may also be removed in the reversed sweep. Theobservation of the more positive potential for the reverse wave isbelieved to reflect the bimetallic effect on the re-activation of thecatalyst surface after the anodic sweep. The re-activation of thesurface catalytic sites after the anodic sweep is likely modified by thepresence of Au in the catalyst. The presence of Au shifts the peakpotential of the reverse wave to a more positive potential byapproximately 200 mV for AuPt/C compared to the Pt/C catalyst.

Depending on the relative Pt concentration in the bimetallicnanoparticles, features that are characteristic of hydrogen adsorptionwaves and hydrogen evolution current may also be seen. These featuresare characteristic of the Pt component in the approximately −0.2 V to0.1 V potential range. These characteristics are also modified by thepresence of Au component. This finding supports the fact that thebimetallic composition of the AuPt nanoparticles is operative inelectrocatalytic reactions.

The electrocatalytic activity of the catalysts loaded on glassy carbonelectrode was also characterized for ORR reaction in both acidic andalkaline electrolytes.

The electrocatalytic properties of carbon-supported Au nanoparticlesAu/C is discussed in copending U.S. patent application Ser. No.11/051,777. With regard to the ORR, an Au/C catalyst (17% wt metal) in0.5 M KOH and 0.5 M H₂SO₄ electrolytes saturated with O₂ shows a largecathodic wave in its CV data. This cathodic wave is approximately −150mV in the alkaline electrolyte and +50 mV in the acidic electrolyte.This is attributable to electrocatalytic O₂ reduction. To evaluate theelectrocatalytic properties, rotating disk electrode (RDE) experimentswere performed to determine the number of electrons transferred in theelectrocatalytic ORR process.

Based on CV data for ORR an Au/C catalyst (17% by weight metal) in 0.5 MKOH and 0.5 M H₂SO₄ electrolytes saturated with O₂, large cathodic wavesare observed at −150 mV in the alkaline electrolyte and at +50 mV in theacidic electrolyte. The waves are attributable to electrocatalytic O₂reduction. To evaluate the electrocatalytic properties, rotating diskelectrode (RDE) experiments were performed to determine the number ofelectrons transferred in the electrocatalytic ORR process. Based onLevich plots of the limiting current vs. rotating speed, an electrontransfer number (n) was derived. A value of n=2.4 was obtained for ORRin 0.5M KOH electrolyte, and 2.2 for ORR in 0.5M H₂SO₄ electrolyte. Thefact that the n values fall between 2 and 4 indicates that theelectrocatalytic ORR at the Au/C catalyst likely involved mixed 2e⁻ and4e⁻ reduction processes.

Referring now to FIGS. 9 a and 9 b, there are shown typical sets of CVcurves for Au₇₂Pt₂₈/C catalysts treated at 400° C. and 500° C.,respectively. Data are provided for both alkaline and acidicelectrolytes. Two important pieces of evidence support the presence ofboth Au and Pt on the surface of the nanoparticle catalyst. First, theoxidation-reduction wave of gold oxide at approximately 200 mV at theAu₇₂Pt₂₈/C catalyst in the O₂-free alkaline electrolyte (FIG. 9 a) is aclear indication of the presence of Au on the catalyst surface. Second,the hydrogen reduction-oxidation currents at −200 mV in the O₂-freeacidic electrolyte (FIG. 9 b) is characteristic of hydrogen adsorptionand reduction at Pt electrodes, provides strong evidence of the presenceof Pt on the catalyst surface.

The observation that the Au₇₂Pt₂₈/C catalyst treated at 500° C. displaysmore features characteristic of Au redox reaction than the Au₇₂Pt₂₈/Ccatalyst treated at 400° C. is indicative of the differences in surfacebimetallic composition. These differences suggest that there is asignificant fraction of Au on the bimetallic catalyst which keeps thenanoscale gold property unchanged in a basic electrolyte, but modifiesthe catalytic property of Pt in an acidic electrolyte.

From RDE data obtained for an ORR with an Au₇₂Pt₂₈/C catalyst treated at400° C. and Levich plots, the value for the electron transfer number (n)may be derived. The results showed that n=3.1±0.4 in 0.5 M KOH and2.9±0.4 in 0.5 M H₂SO₄. For the same Au₇₂Pt₂₈/C catalyst treated at 500°C., n=2.5±0.4 in 0.5 M H₂SO₄ and 2.6 in 0.5 M H₂SO₄. There is anoticeable increase in the n value for the bimetallic AuPt/C catalysttreated at 400° C. in comparison with that for the monometallic Au/Ccatalyst. For the Au₇₂Pt₂₈/C catalyst treated at 500° C., the resultsshow n=3.0 in 0.5 M KOH and 3.1 in 0.5 M H₂SO₄ for an ORR. These valuesare somewhat larger than those obtained for an Au/C catalyst. Again, theAu₇₂Pt₂₈/C catalyst treated at 500° C. seems to display more featurescharacteristic of Au.

The electrochemical data for Au/C (20% metals) and AuPt/C catalysts (20%metals) were compared with those obtained from characterizations ofcommercially-available catalysts, namely E-tek's Pt/C (20% metals) andPtRu/C catalysts (20% metals). The electrocatalytic ORR data wereobtained at E-tek's Pt/C catalysts (20% metals) in both alkaline andacidic electrolytes.

The Levich plot analysis of the RDE data for the ORR of E-tek's Pt/Ccatalyst (20% wt) in acidic electrolyte reveal n=4.0±0.2, consistentwith a 4e⁻ process for the reduction of O₂ to H₂O at the Pt catalyst.Similar results are obtained for an ORR in the alkaline electrolyte. Incomparison with the Pt/C data, the n values obtained with our Au/C andAuPt/C catalysts are between approximately 3.0-3.6, displaying anincrease of n with increasing Pt composition in the bimetallicnanoparticles. The fact that the obtained n values fall between n=2 andn=4 likely suggests that both 2e⁻ reduction to H₂O₂ and 4e⁻ reduction toH₂O processes are operative with the catalysts. One possible explanationmay be the presence of large-sized particles in the thermally treatedcatalysts. A further delineation of the surface composition, particlesize and treatment condition are expected to provide more insights intothe detailed catalytic mechanism.

One important discovery is that the electrocatalytic activity for thebimetallic AuPt catalysts falls between that of Au and Pt catalysts.This may be seen in FIGS. 10 a and 10 b which show data obtained fromRDE measurements for an ORR for three different catalysts, Au/C, Pt/C,and Au₇₂Pt₂₈/C.

In addition to exploring similar pathways for high-throughput screeningof combinatorial array catalysts as demonstrated by others,combinatorial analysis was applied to a limited number of experimentsfor optimization and directing further experiments in the preparation ofbest catalysts. This focus is largely based on unique approach of thepresent invention to the design of size-, composition- andphase-controllable catalysts at the nanoscale which involves synthesis,processing, assembly and thermal treatment.

Both Au_(n)Pt_(100-n) and Au_(n)Pt_(m)Fe_(100-m-n) catalysts arecompared to evaluate their electrocatalytic activities for ORR and MOR.FIGS. 11 a-11 b and Tables 3-4 illustrate a few examples.

FIGS. 11 a-11 b compares the RDE data for ORR at severalAu_(n)Pt_(100-n) and Au_(n)Pt_(m)Fe_(100-m-n) catalysts of differentcompositions in an alkaline and an acidic electrolyte, respectively.

The multimetallic nanoparticle catalysts are mixed with Nafion andloaded on glassy carbon electrode for MOR and ORR electrochemicalcharacterizations. Both current (i_(p)) and Tafel analysis provide datafor assessing the electrocatalytic activity for MOR, whereas the kineticcurrent (i₁) from the RDE data and Tafel analysis data provide measuresfor assessing the electrocatalytic activity for ORR. Tables 3 and 4summarizes two sets data for the AuPt/C and AuPtFe/C catalysts for MORin 0.5 M KOH and ORR in 0.5 M KOH and 0.5 M H₂SO₄. The data are alsocompared with commercially-available catalysts (e.g., E-tek'scatalysts).

TABLE 3 Electrocatalytic MOR activities in 0.5 M KOH T_(c) = 400° C.T_(c) = 500° C. T_(c) = 600° C. Catalyst/C TS i_(pa) TS i_(pa) TS i_(pa)Au  349 Pt 8092 Au₉₇Pt₃ 106 1869 Au₈₂Pt₁₈ 127 6518 149 8536 Au₇₂Pt₂₈ 1552821 148 5291 Au₆₅Pt₃₅ 106 7875 Au₆₀Pt₄₀ 165 4482 Au₅₆Pt₄₄ 154  855 1014432 120 4078 Au₅₀Pt₆₅ 4884 Au₁₁Pt₂₃Fe₆₆ 130 1215 154  729

TABLE 4 ORR activities in 0.5 M KOH and 0.5 M H₂SO₄ saturated with O₂ In0.5 M KOH In 0.5 M H₂SO₄ Catalyst/ T_(c) = 400° C. T_(c) = 500° C. T_(c)= 600° C. T_(c) = 400° C. T_(c) = 500° C. T_(c) = 600° C. C TSI_(E=−0.1V) TS I_(E=−0.1V) TS I_(E=−0.1V) TS I_(E=0.55V) TS I_(E=0.55V)TS I_(E=0.55V) Au 55.8 124 143.6 7 Pt 52.2 62 86.1 432 Au₉₇Pt₃ 55.9 95161.2 9 Au₈₂Pt₁₈ 116 8 Au₇₂Pt₂₈ 67.0 125 54.8 180 116.1 32 108.3 37Au₆₅Pt₃₅ 59.9 110 112.3 63 Au₅₆Pt₄₄ 51.1 54 59.5 54 56.7 8 88.0 190 96.3203 89.1 127 Au₃₅Pt₆₅ 73 100 Au₁₁Pt₂₃Fe₄₆ 47.6 332 49.5 76 65.3 386 63.6347 Note The mass activity I_(g) (mA/cm²/mg Mt) was obtained form RDEkinetic current at E and 1600 rpm, 5 mV/s. Catalyst metal loading: 20%.Mt: total metals. TS: Tafel slope (mV/dec); T_(c): thermal treatmenttemperature. (Reference electrode: Ag/AgCl, Sat'd KCl)

The results demonstrate that the composition can significantly modifythe electrocatalytic properties of both Au and Pt. The bimetallic alloyAuPt nanoparticle catalysts exhibit a synergistic activity which dependsnot only on the composition, but also on the nature of the electrolyte.For MOR, the mass activity in the alkaline electrolyte exhibits amaximum in the composition region of 65˜85% Au, in contrast to thegradual increase from no activity of Au to a high activity of Pt in theacidic electrolyte. For ORR, the mass activities displays a maximum inthe composition region of 60-80% Au, which is higher than Pt/C and Au/Cby a factor of 2-3, in contrast to the gradual increase from a smallactivity of Au to a high activity of Pt in the acidic electrolyte. TheAu-based bimetallic and trimetallic nanoparticle catalysts supported oncarbon materials are electrocatalytically active for both MOR and ORRreactions, depending on the nature of the electrolytes and thetemperature used for the thermal treatment. In alkaline condition, thebinary and the ternary catalysts serve as good catalysts for MOR andORR. In acidic condition, the catalysts serve as good catalysts for ORR.In addition to be CO-tolerant because of the presence of gold in thecatalysts, the catalysts not only reduce the possibility of OH⁻adsorption on the catalysts but also increase the tolerance of methanol.

The method of the present invention teaches preparation of gold-basedmonometallic, bimetallic and trimetallic nanoparticles havingmonodispersed sizes and controlled compositions. These nanoparticles areuseful as MOR and ORR electrocatalysts. The nanoparticle compositionscan significantly modify the electrocatalytic properties of both Au andPt. The approach is useful for developing effective gold-based catalystsfor improving fuel cell anode and cathode reactions. Specifically,carbon-supported Au nanoparticle catalysts which can be treated undercontrolled conditions have been prepared.

Several protocols for synthesizing Au-based bimetallic and trimetallicnanoparticles using chemical reduction coupled to thermal decompositionare provided. In addition, bimetallic nanoparticle catalysts aftercontrolled treatment are shown to be single-phase alloys. It has alsobeen shown that Au-based monometallic, bimetallic and trimetallicnanoparticle catalysts supported on carbon materials areelectrocatalytically active towards both MOR and ORR reactions. Further,it has been shown that the catalytic activity of the bimetallic andtrimetallic catalysts is dependent on the temperature used for thethermal treatment.

Since other modifications and changes varied to fit particular operatingrequirements and environments will be apparent to those skilled in theart, the invention is not considered limited to the examples chosen forpurposes of disclosure, and covers all changes and modifications whichdo not constitute departures from the true spirit and scope of thisinvention.

Having thus described the invention, what is desired to be protected byLetters Patent is presented in the subsequently appended claims.

1. A fuel cell catalyst comprising: a particulate support and goldcore-shell nanoparticles having a formula of Au_(y)Pt_(z)M_(100−(y+z)),wherein y and z are integers between 1 and 99, and M is at least onemetal selected from the group consisting of Ti, Cr, Mn, Fe, and W,wherein the shells of said gold core-shell nanoparticles remain intactand are responsible for interaction with said particulate support. 2.The fuel cell catalyst as recited in claim 1, wherein said particulatesupport is selected from the group consisting of carbon, silicon, andcombinations thereof.
 3. The fuel cell catalyst as recited in claim 2,wherein said particulate support is in the form of carbon spheres havingdiameters in approximately the 10-1000 nm range.
 4. The fuel cellcatalyst as recited in claim 1, wherein said core-shell nanoparticlescomprise alkanethiolate shells.
 5. The fuel cell catalyst as recited inclaim 3, wherein said carbon spheres have diameters in the range of30-50 nm.
 6. The fuel cell catalyst as recited in claim 1, wherein thenanoparticles have a relative size monodispersity of ±0.6 nm.